This will be key. I know in the past when the US and Mexico have been invited they've typically sent younger sides. They need to get the dates worked out and make sure they are on the same page as FIFA so the best players will be available.

It'll be beneficial to send our A team. For South American teams, this is a high respected tournament. Add the fact that this is older than European Championship.
Rio game will be U-23 only plus 3 "over-age" players. So there shouldn't be huge conflicts with the availability of the players.